I have several B5C’s + Rocket dish links with RF Cables from 36" to 120" in length no problem. I think it’s probably not a great idea to go 120" but I had no other option, and it’s probably a bad idea to have the two RF Cables of different lengths and quality. The links are from 7km to 37km no problem.
Check the ‘ring’ on the RF ports on the neck of the Rocket dish. It has a notch in it. Use a small screwdriver to give that ring another 1/2 to 3/4 of a turn. I’ve found in the past that those rings can be very loose and will stop the barrel connector from actually making contact with the port. Also make sure your barrel connectors are Straight and not stressed from the RF Cable.
Polarity miss match is not an issue now on 1.4.1 when using Dual slant.
You did test this on the bench to be sure that they could link before deploying them right ?